Instead, we are left with the young Takeda's mysterious learning experience with the Shinto scholar, Tanamo Saigo (AKA Hoshino Genshin) who, as with other high-born Japanese scholars of the day, was well versed in Chinese classical literature, ranging from Taoist texts to Confucian and possibly other estorica that may or may not have included certain esoteric internal exercises (qigong, neigong) the Chinese got, in ancient days, from Indian Buddhist and Tantric monks.

What if it wasn't really that secret at all, but was simply esoteric knowledge that made a somewhat clunky, innappropriate fit to martial applications due to steep learning curve and not much usefulness versus the time and resources required for training? Until the Meiji period when there was no longer a caste of professional warriors who needed real combat skills to keep society functioning?